One way that a wireless cellular service provider can improve the coverage provided by a given base station or group of base stations is by using a distributed antenna system (DAS). In a DAS, radio frequency (RF) signals are communicated between a hub unit and one or more remote antenna units (RAUs). The hub unit can be communicatively coupled to one or more base stations directly by connecting the hub unit to the base station using, for example, coaxial cabling. The hub unit can also be communicatively coupled to one or more base stations wirelessly, for example, using a donor antenna and a bi-directional amplifier (BDA).
RF signals transmitted from the base station (also referred to here as “downlink RF signals”) are received at the hub unit. The hub unit uses the downlink RF signals to generate a downlink transport signal that is distributed to one or more of the RAUs. Each such RAU receives the downlink transport signal and reconstructs the downlink RF signals based on the downlink transport signal and causes the reconstructed downlink RF signals to be radiated from at least one antenna coupled to or included in that RAU. A similar process is performed in the uplink direction. RF signals transmitted from mobile units (also referred to here as “uplink RF signals”) are received at each RAU. Each RAU uses the uplink RF signals to generate an uplink transport signal that is transmitted from the RAU to the hub unit. The hub unit receives and combines the uplink transport signals transmitted from the RAUs. The hub unit reconstructs the uplink RF signals received at the RAUs and communicates the reconstructed uplink RF signals to the base station. In this way, the coverage of the base station can be expanded using the DAS.
One or more intermediate devices (also referred to here as “expansion hubs” or “expansion units”) can be placed between the hub unit and the remote antenna units in order to increase the number of RAUs that a single hub unit can feed and/or to increase the hub-unit-to-RAU distance.
Some DAS systems incorporate automatic gain control functionality to automatically adjust the gain and slope of the RF signals. In systems that support only one or two bi-directional RF bands (each RF band including a respective downlink RF band and respective uplink RF band), such automatic gain control is performed on each RF band separately. However, in systems that support a relatively large number of RF bands (for example, eight RF bands), performing automatic gain control on a band-by-band basis can increase the cost and complexity of the DAS system significantly.